Simplify some of the startup code for SubStringStub::Generate.

src/arm/simulator-arm.cc

Index: src/arm/simulator-arm.cc
diff --git a/src/arm/simulator-arm.cc b/src/arm/simulator-arm.cc
index 91df404f9af3a00a191d8d232d4c5858e4d3155b..578dc4329bd4f2c05b537ad79b0e05303d1a1268 100644
--- a/src/arm/simulator-arm.cc
+++ b/src/arm/simulator-arm.cc
@@ -1426,7 +1426,14 @@ int32_t Simulator::GetShiftRm(Instruction* instr, bool* carry_out) {
       }
 
       case ROR: {
-        UNIMPLEMENTED();
+        if (shift_amount == 0) {
+          *carry_out = c_flag_;
+        } else {
+          uint32_t left = static_cast<uint32_t>(result) >> shift_amount;
+          uint32_t right = static_cast<uint32_t>(result) << (32 - shift_amount);
+          result = right | left;
+          *carry_out = (static_cast<uint32_t>(result) >> 31) != 0;
+        }
         break;
       }